Display device

ABSTRACT

A display device according to the present invention includes a barrier layer formed over the transistor and a planarization layer formed over the barrier layer. The planarization layer has an opening and an edge portion of the planarization layer formed at the opening of the planarization layer is rounded. Further, a resin film is formed over the planarization layer and in the opening of the planarization layer, and the resin film also has an opening and an edge portion of the resin film formed at the opening of the resin film is rounded. A light emitting member is formed over the resin film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention belongs to a technical field related to a displaydevice in which a semiconductor device (typically, a transistor) is usedas a device, in particular, a light emitting device represented by anelectroluminescence display device, and to a technical field related toan electronic apparatus equipped with the display device in an imagedisplay portion.

2. Description of the Related Art

In recent years, development of liquid crystal display devices andelectroluminescence display devices in which transistors (particularly,thin film transistors) are integrated on a substrate have progressed.Such display devices are respectively characterized in that thetransistors are formed on a glass substrate by using a thin filmformation technique, and the transistors thus formed are disposed inpixels each arranged in matrix and made to function as a display devicefor image display.

A variety of specifications are conceivable, which are required forareas (hereinafter, referred to as pixel portions), in which the imagedisplay is performed in the display device. However, the following aregiven as examples thereof: a large number of dots and high definitionare ensured; an area of an effective display region in each pixel islarge and bright image display is possible; and the pixel portioninvolves no defects that may induce point defects or line defects in itsentirety. In order to achieve those specifications, not only theperformance of the transistors arranged in each pixel should besatisfactory but also a technique of forming the transistors whileincreasing yield through a stable process is necessary.

Further, in an organic electroluminescence display device among theelectroluminescence display devices, an organic compound is used for alight emitting element serving as a light emitting source. Accordingly,a measure for suppressing deterioration of the organic compound is mosthighly required in ensuring its reliability. In other words, in order toachieve a highly reliable display device, attention must be paid notonly to an influence of an accumulated damage in the process duringmanufacturing the device but also to the subsequent deterioration withtime, which results from the accumulated damage.

In the above-mentioned circumstances of development, the applicants ofthe present invention are most concerned, in the present conditions,with problems such as variation and shift of a threshold voltage in thetransistors, which arise due to the accumulation of plasma damages on aninsulating film etc. in an etching process.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedproblems and an object of the present invention is to provide a devicestructure effective in reducing an influence of plasma damage in amanufacturing process of a display device. Further, another object ofthe present invention is to provide a display device having uniformdisplay characteristics (referring to display characteristics small inluminance variation between adjacent pixels and in degradation degree)obtained by reducing the influence of the plasma damage to suppressvariations in threshold voltage of transistors.

The present invention relates to a display device characterized byincluding the following structures as a device structure effective insolving the above problems. Note that a light emitting element definedhere refers to an element in which a light emitting member (referring toa laminate obtained by laminating a light emitting layer, a carrierinjecting layer, a carrier transporting layer, a carrier blocking layer,and other components required for light emission, such as an organic orinorganic compound) is provided between a pair of electrodes (anode andcathode). For example, an electroluminescence element is included in thecategory of the light emitting element.

-   (1) A display device according to the present invention includes:

a transistor formed on a substrate surface; and

a light emitting element connected with the transistor,

the transistor including:

-   -   an active layer formed of a semiconductor;    -   a gate insulating film formed in contact with the active layer;    -   a gate electrode facing the active layer through the gate        insulating film;    -   a barrier layer formed above the active layer;    -   a planarization layer formed on the barrier layer; and    -   a drain electrode formed on the planarization layer,

the light emitting element including:

-   -   a pixel electrode connected in contact with an upper surface of        the drain electrode on the planarization layer;    -   a light emitting member formed in contact with the pixel        electrode; and    -   an opposing electrode facing the pixel electrode through the        light emitting member, and

the drain electrode being connected with the active layer through afirst opening formed in the gate insulating film and the barrier layerand a second opening formed in the planarization layer.

Note that the planarization layer of the present invention may be formedof either an inorganic insulating film or an organic resin film formedby sputtering, plasma CVD, low-pressure thermal CVD, or spin-coating.Also, when the planarization layer is formed by sputtering, plasma CVD,or low-pressure thermal CVD, its surface may be polished before the use(inclusive of polishing with a mechanical or chemical action, or acombined action thereof). By using the planarization layer, the surfaceof a first electrode formed on the planarization layer can be leveledand the light emitting element (EL element) can be prevented from beingshort-circuited. Also, by providing the barrier layer thereon, impuritydiffusion from the EL element can be blocked to protect TFTs anddegassing from an organic insulating film can be avoided as well.Further, by forming the barrier layer in the portion close to the activelayer of the TFT, the impurity diffusion from the EL element is blockedto effectively protect the TFT.

-   (2) A display device according to the present invention includes:

a transistor formed on a substrate surface; and

a light emitting element connected with the transistor,

the transistor including:

-   -   an active layer formed of a semiconductor;    -   a gate insulating film formed in contact with the active layer;    -   a gate electrode facing the active layer through the gate        insulating film;    -   a planarization layer formed above the active layer;    -   a barrier layer formed on the planarization layer; and    -   a drain electrode formed on the barrier layer,

the light emitting element including:

-   -   a pixel electrode connected in contact with an upper surface of        the drain electrode on the planarization layer;    -   a light emitting member formed in contact with the pixel        electrode; and    -   an opposing electrode facing the pixel electrode through the        light emitting member,

the drain electrode being connected with the active layer through afirst opening formed in the gate insulating film and the barrier layerand a second opening formed in the planarization layer, and

the barrier layer covering an upper surface of the planarization layerand a side surface of the second opening formed in the planarizationlayer.

Also, according to the structure stated in (2), the barrier layer isformed to thereby prevent the planarization layer from being etched inetching the first electrode and the drain electrode. Also, by coveringthe planarization layer with the barrier layer, the impurity diffusionfrom the planarization layer to the light emitting element is avoided.

-   (3) A display device according to the present invention includes:

a transistor formed on a substrate surface; and

a light emitting element connected with the transistor,

the transistor including:

-   -   an active layer formed of a semiconductor;    -   a gate insulating film formed in contact with the active layer;    -   a gate electrode facing the active layer through the gate        insulating film;    -   a planarization layer formed above the active layer;    -   a barrier layer formed on the planarization layer; and    -   a drain electrode formed on the barrier layer,

the light emitting element including:

-   -   a pixel electrode connected in contact with an upper surface of        the drain electrode on the planarization layer;    -   a light emitting member formed in contact with the pixel        electrode; and    -   an opposing electrode facing the pixel electrode through the        light emitting member,

the drain electrode being connected with the active layer through anopening formed in the gate insulating film, the planarization layer, andthe barrier layer, and

the barrier layer covering an upper surface of the planarization layer.

Also, according to the structure stated in (3), the openings formed inthe gate insulating film, the planarization layer, and the barrier layerare formed through etching by use of the same masks and can thus beformed with the smaller number of masks than that of the structure in(1) or (2).

-   (4) A display device according to the present invention includes:

a transistor formed on a substrate surface; and

a light emitting element connected with the transistor,

the transistor including:

-   -   an active layer formed of a semiconductor;    -   a gate insulating film formed in contact with the active layer;    -   a gate electrode facing the active layer through the gate        insulating film;    -   a barrier layer formed above the active layer;    -   a planarization layer formed on the barrier layer; and    -   a drain electrode formed on the planarization layer,

the light emitting element including:

-   -   a pixel electrode connected in contact with a lower surface of        the drain electrode on the planarization layer;    -   a light emitting member formed in contact with the pixel        electrode; and    -   an opposing electrode facing the pixel electrode through the        light emitting member, and

the drain electrode being connected with the active layer through afirst opening formed in the gate insulating film and the barrier layerand a second opening formed in the planarization layer.

-   (5) A display device according to the present invention includes:

a transistor formed on a substrate surface; and

a light emitting element connected with the transistor,

the transistor including:

-   -   an active layer formed of a semiconductor;    -   a gate insulating film formed in contact with the active layer;    -   a gate electrode facing the active layer through the gate        insulating film;    -   a planarization layer formed above the active layer;    -   a barrier layer formed on the planarization layer; and    -   a drain electrode formed on the barrier layer,

the light emitting element including:

-   -   a pixel electrode connected in contact with a lower surface of        the drain electrode on the planarization layer;    -   a light emitting member formed in contact with the pixel        electrode; and    -   an opposing electrode facing the pixel electrode through the        light emitting member,

the drain electrode being connected with the active layer through afirst opening formed in the gate insulating film and the barrier layerand a second opening formed in the planarization layer, and

the barrier layer covering an upper surface of the planarization layerand a side surface of the second opening formed in the planarizationlayer.

-   (6) A display device according to the present invention includes:

a transistor formed on a substrate surface; and

a light emitting element connected with the transistor,

the transistor including:

-   -   an active layer formed of a semiconductor;    -   a gate insulating film formed in contact with the active layer;    -   a gate electrode facing the active layer through the gate        insulating film;    -   a planarization layer formed above the active layer;    -   a barrier layer formed on the planarization layer; and    -   a drain electrode formed on the barrier layer,

the light emitting element including:

-   -   a pixel electrode connected in contact with a lower surface of        the drain electrode on the planarization layer;    -   a light emitting member formed in contact with the pixel        electrode; and    -   an opposing electrode facing the pixel electrode through the        light emitting member,

the drain electrode being connected with the active layer through anopening formed in the gate insulating film, the planarization layer, andthe barrier layer, and

the barrier layer covering an upper surface of the planarization layer.

Also, according to the structures stated in (4), (5), and (6), afterforming the pixel electrode, the drain electrode is formed, so that thestructures are useful in the case where the drain electrode has a largefilm thickness. When formed after the formation of the drain electrode,the pixel electrode is needed to partially overlap the drain electrode.When the drain electrode has a large film thickness, there is a fearthat any coverage failure takes place, such as step-like breakage in thepixel electrode.

-   (7) A display device according to the present invention includes:

a transistor formed on a substrate surface; and

a light emitting element connected with the transistor,

the transistor including:

-   -   an active layer formed of a semiconductor;    -   a gate insulating film formed in contact with the active layer;    -   a gate electrode facing the active layer through the gate        insulating film;    -   a barrier layer formed above the active layer;    -   an insulating layer formed on the barrier layer;    -   a drain electrode formed on the insulating layer; and    -   a planarization layer formed on a source electrode or the drain        electrode,

the light emitting element including:

a pixel electrode formed on the planarization layer and connected withthe drain electrode through an opening formed in the planarizationlayer;

-   -   a light emitting member formed in contact with the pixel        electrode; and    -   an opposing electrode facing the pixel electrode through the        light emitting member, and

the drain electrode being connected with the active layer through afirst opening formed in the gate insulating film and the barrier layerand a second opening formed in the insulating layer.

-   (8) A display device according to the present invention includes:

a transistor formed on a substrate surface; and

a light emitting element connected with the transistor,

the transistor including:

-   -   an active layer formed of a semiconductor;    -   a gate insulating film formed in contact with the active layer;    -   a gate electrode facing the active layer through the gate        insulating film;    -   an insulating layer formed above the active layer;    -   a barrier layer formed on the insulating layer;    -   a drain electrode formed on the barrier layer; and    -   a planarization layer formed on the drain electrode,

the light emitting element including:

-   -   a pixel electrode formed on the planarization layer and        connected with the drain electrode through an opening formed in        the planarization layer;    -   a light emitting member formed in contact with the pixel        electrode; and    -   an opposing electrode facing the pixel electrode through the        light emitting member,

the drain electrode being connected with the active layer through afirst opening formed in the gate insulating film and the barrier layerand a second opening formed in the insulating layer, and

the barrier layer covering an upper surface of the insulating layer anda side surface of the second opening formed in the insulating layer.

-   (9) A display device according to the present invention includes:

a transistor formed on a substrate surface; and

a light emitting element connected with the transistor,

the transistor including:

-   -   an active layer formed of a semiconductor;    -   a gate insulating film formed in contact with the active layer;    -   a gate electrode facing the active layer through the gate        insulating film;    -   an insulating layer formed above the active layer;    -   a barrier layer formed on the insulating layer;    -   a drain electrode formed on the barrier layer; and    -   a planarization layer formed on the drain electrode,

the light emitting element including:

-   -   a pixel electrode formed on the planarization layer and        connected with the drain electrode through an opening formed in        the planarization layer;    -   a light emitting member formed in contact with the pixel        electrode; and    -   an opposing electrode facing the pixel electrode through the        light emitting member,

the drain electrode being connected with the active layer through anopening formed in the gate insulating film, the insulating layer, andthe barrier layer, and

the barrier layer covering an upper surface of the insulating layer.

Further, according to the structures stated in (7), (8), and (9), thepixel electrode is connected with the drain electrode through a contacthole and insulated from the other wirings through the planarizationlayer, so that the area of the pixel electrode can be increased.

Note that, according to the structures stated in (7) to (9), the uppersurface of the planarization layer may be covered with the siliconnitride film. This is because when the organic resin film is used as theplanarization layer, in particular, the upper surface thereof (includingan inner wall surface thereof when any opening is formed) is coveredwith the silicon nitride film, so that gases (including a component gasor moisture) generated from the organic resin film can be effectivelyprevented from diffusing to the light emitting element side.

Also, it is preferable that end portions (at least, corner portions) ofthe pixel electrode be covered with the resin film. This is because theelectric fields are likely to concentrate in the end portion of thepixel electrode and further, coverage of the film formed thereon ispoor, so that it is preferable not to use the end portions in formingthe light emitting element. Note that the resin film may be either anonphotosensitive resin film or a photosensitive resin film. If usingthe photosensitive resin film, either positive or negative type filmscan be used.

-   (10) A display device according to the present invention includes:

a transistor formed on a substrate surface; and

a light emitting element connected with the transistor,

the transistor including:

-   -   an active layer formed of a semiconductor;    -   a gate insulating film formed in contact with the active layer;    -   a gate electrode facing the active layer through the gate        insulating film;    -   a barrier layer formed above the active layer;    -   a planarization layer formed on the barrier layer; and    -   a drain electrode formed on the planarization layer,

the drain electrode constituting a laminate electrode having a laminatestructure of a first metallic film and a second metallic film andincluding a portion where a part of the second metallic film is removedto expose the first metallic film,

the light emitting element including:

-   -   the portion where the first metallic film is exposed;    -   a light emitting member formed in contact with the portion where        the first metallic film is exposed; and    -   an opposing electrode facing the portion where the first        metallic film is exposed through the light emitting member, and

the drain electrode being connected with the active layer through afirst opening formed in the gate insulating film and the barrier layerand a second opening formed in the planarization layer.

-   (11) A display device according to the present invention includes:

a transistor formed on a substrate surface; and

a light emitting element connected with the transistor,

the transistor including:

-   -   an active layer formed of a semiconductor;    -   a gate insulating film formed in contact with the active layer;    -   a gate electrode facing the active layer through the gate        insulating film;    -   a planarization layer formed above the active layer;    -   a barrier layer formed on the planarization layer; and    -   a drain electrode formed on the barrier layer,

the drain electrode constituting a laminate electrode having a laminatestructure of a first metallic film and a second metallic film andincluding a portion where a part of the second metallic film is removedto expose the first metallic film,

the light emitting element including:

-   -   the portion where the first metallic film is exposed;    -   a light emitting member formed in contact with the portion where        the first metallic film is exposed; and    -   an opposing electrode facing the portion where the first        metallic film is exposed through the light emitting member, and

the barrier layer covering an upper surface of the planarization layerand a side surface of an opening formed in the insulating layer.

-   (12) A display device according to the present invention includes:

a transistor formed on a substrate surface; and

a light emitting element connected with the transistor,

the transistor including:

-   -   an active layer formed of a semiconductor;    -   a gate insulating film formed in contact with the active layer;    -   a gate electrode facing the active layer through the gate        insulating film;    -   a planarization layer formed above the active layer;    -   a barrier layer formed on the planarization layer; and    -   a drain electrode formed on the barrier layer,

the drain electrode constituting a laminate electrode having a laminatestructure of a first metallic film and a second metallic film andincluding a portion where a part of the second metallic film is removedto expose the first metallic film,

the light emitting element including:

-   -   the portion where the first metallic film is exposed;    -   a light emitting member formed in contact with the portion where        the first metallic film is exposed; and    -   an opposing electrode facing the portion where the first        metallic film is exposed through the light emitting member,

a source electrode and the drain electrode being connected with theactive layer through an opening formed in the gate insulating film, theinsulating layer, and the barrier layer, and

the barrier layer covering an upper surface of the planarization layer.

Note that, according to the structures stated in (10) to (12), an anglebetween a section of the second metallic film in the portion where apart of the second metallic film is removed to expose the first metallicportion and an upper surface of the second metallic film is preferablyan obtuse angle. In other words, the above means that the portionconcerned is formed by removing the second metallic film through etchingand etching is preferably performed such that the etched section takes atapered shape. This is because even when the light generated inside thelight emitting member propagates laterally in the light emitting member,the light can be reflected by the section and taken out efficiently,provided that the section of the second metallic film has the taperedshape. According to the structures stated in (10) to (12), the emittedlight in the lateral direction is reflected by the slope of the secondmetallic film formed in the step portion of the laminate electrode orcondensed there, thereby increasing an amount of the emitted light thatis to be taken out in a certain direction (direction in which the lightpasses through the opposing electrode). Also, for that purpose, it ispreferable that the film thickness of the light emitting member besmaller than that of the second metallic film.

Further, the pixel portion is covered with the resin film except theportion where a part of the second metallic film is removed to exposethe first metallic film. This is because the second metallic film isetched by using the resin film, so that the portions other than a partof the second metallic film (removed portion) are all covered with theresin film. However, the resin film is only needed to cover the pixelportion and it is not always required for the resin film to remain inthe portions other than the pixel portion (e.g., driver circuitportion). Further, needless to say, a terminal portion fortransmitting/receiving signals to/from an external circuit should beuncovered with the resins film.

Note that the first metallic film is preferably made of a metallic filmcapable of functioning as an anode of the light emitting element, suchas a titanium film or a titanium nitride film. The second metallic filmis preferably made of a metallic film such as an aluminum film(including an aluminum alloy film or an aluminum film added with otherelements, the same being applied to the following description), whichshows high reflectivity. In this example, only a two-layer structurecomposed of the first metallic film and the second metallic film isshown, but the multi-layer structure including the two or more layerscan be adopted.

In the above structures of the present invention, the silicon nitridefilm used for the barrier layer is preferably made as fine as possible.The higher the fineness, the higher the barrier property. The diffusionblocking effect against the degassing component is thus enhanced. Forexample, when the organic resin film is used as the planarization layer,the diffusion of the component gas or moisture therefrom to thetransistor side or the light emitting element side can be effectivelysuppressed.

Further, when the inorganic insulating film (typically, a spin on glassfilm) formed by spin-coating is used as the planarization layer as well,the above is rather extremely effective in controlling the diffusion ofthe component gas or moisture. Further, the SOG (spin on glass) filmincludes an organic SOG film and an inorganic SOG film. When consideringthe application to the present invention, the inorganic SOG film ispreferable because of less degassing. Preferable examples of theinorganic SOG film include an SiOx film, a PSG (phosphorous silicateglass) film, a BSG (boron silicate glass) film, and a BPSG (boronphosphorous silicate glass) film, which are formed by spin-coating.Specifically, the SOG film is represented by OCD series manufactured byTokyo Ohka Kogyo Co., Ltd.) and it is needless to say that the otherknown SOG films can be used.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1D are a top view, a circuit diagram, and sectional viewsfor showing a device structure of a display device;

FIGS. 2A and 2B are sectional views for showing a device structure of adisplay device;

FIGS. 3A and 3B are sectional views for showing a device structure of adisplay device;

FIGS. 4A and 4B are sectional views for showing a device structure of adisplay device;

FIGS. 5A to 5C are sectional views for showing a device structure of adisplay device;

FIGS. 6A to 6C are sectional views for showing a device structure of adisplay device;

FIGS. 7A to 7C are sectional views for showing a device structure of adisplay device;

FIGS. 8A to 8C are sectional views for showing a device structure of adisplay device;

FIGS. 9A to 9D are a top view, a circuit diagram, and sectional viewsfor showing a device structure of a display device;

FIGS. 10A and 10B are sectional views for showing a device structure ofa display device;

FIGS. 11A and 11B are sectional views for showing a device structure ofa display device;

FIGS. 12A and 12B are sectional views for showing a device structure ofa display device;

FIGS. 13A to 13C are sectional views for showing a device structure of adisplay device;

FIGS. 14A to 14D are a top view, a circuit diagram, and sectional viewsfor showing a device structure of a display device;

FIGS. 15A and 15B are sectional views for showing a device structure ofa display device;

FIGS. 16A and 16B are sectional views for showing a device structure ofa display device;

FIGS. 17A and 17B are sectional views for showing a device structure ofa display device;

FIGS. 18A to 18C are sectional views for showing a device structure of adisplay device;

FIGS. 19A and 19B are a top view and a circuit diagram, respectively,for showing a device structure of a display device;

FIGS. 20A to 20C are sectional views for showing a device structure of adisplay device;

FIGS. 21A and 21B are sectional views for showing a device structure ofa display device;

FIGS. 22A and 22B are sectional views for showing a device structure ofa display device;

FIGS. 23A to 23C are sectional views for showing a device structure of adisplay device;

FIGS. 24A and 24B show a transmission electron microscope photograph ofa structure of a pixel electrode;

FIGS. 25A and 25B are sectional views for showing a device structure ofa display device;

FIGS. 26A and 26B are sectional views for showing a device structure ofa display device;

FIGS. 27A and 27B are sectional views for showing a device structure ofa display device;

FIGS. 28A to 28D are a top view and sectional views for showing an outerappearance of a display device; and

FIGS. 29A to 29H each show an example of electronic apparatuses.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

In this embodiment, an example of an electroluminescence display deviceof the present invention will be described. FIG. 1A is a top view of apixel of the electroluminescence display device (note that a state up tothe formation of a pixel electrode is indicated), FIG. 1B is a circuitdiagram thereof, and FIGS. 1C and 1D each are a cross sectional viewalong a line A-A′ or B-B′.

As shown in FIGS. 1A and 1B, a pixel portion of the electroluminescencedisplay device includes a plurality of pixels which are surrounded bygate wirings 151, data wirings 152, and power source wirings (wiringsfor supplying a constant voltage or a constant current) 153 and arrangedin matrix. In each of the pixels, a TFT 154 serving as a switchingelement (hereinafter referred to as a switching TFT), a TFT 155 servingas means for supplying a current or a voltage for producing lightemission of an light emitting element (hereinafter referred to as adriver TFT), a capacitor portion 156, and an light emitting element 157are provided. Although not shown here, the light emitting element 157can be formed by providing a light emitting layer over a pixel electrode158.

Note that, in this embodiment, an n-channel TFT having a multi-gatestructure is used as the switching TFT 154 and a p-channel TFT is usedas the driver TFT 155. However, the pixel structure of the lightemitting device is limited to this. Thus, the present invention can beapplied to any known structure.

In the cross sectional view of FIG. 1C, the n-channel TFT 154 and thecapacitor portion 156 are shown. Reference numeral 101 denotes asubstrate, and a glass substrate, a ceramic substrate, a quartzsubstrate, a silicon substrate, or a plastic substrate (including aplastic film) can be used. In addition, reference numeral 102 denotes asilicon oxynitride film, 103 denotes a silicon oxynitride film, allwhich are laminated to serve as base films. Of course, the presentinvention is limited to these materials. Further, an active layer of then-channel TFT 154 is provided on the silicon oxynitride film 103. Theactive layer has a source region 104, a drain region 105, LDD regions106 a to 106 d, and channel formation regions 107 a and 107 b. In otherwords, it has two channel formation regions and four LDD regions betweenthe source region 104 and the drain region 105.

Also, the active layer of the n-channel TFT 154 is covered with a gateinsulating film 108, and a gate electrode (gate electrode layers 109 aand 109 b) and another gate electrode (gate electrode layers 110 a and110 b) are provided thereon. In this embodiment, a silicon oxynitridefilm is used as the gate insulating film 108. When the above nitrideinsulating film such as an aluminum nitride film having a high relativedielectric constant is used, an occupying area of an element can bereduced. Thus, it is effective for the improvement of the scale ofintegration.

Also, a tantalum nitride film is used for the gate electrode layers 109a and 110 a and a tungsten film is used for the gate electrode layers109 b and 110 b. With respect to these metallic films, a selection ratiois high. Thus, such a structure can be obtained by selecting an etchingcondition. The etching condition is preferably referred to US2001/0030322 according to the present applicant.

Also, a silicon nitride film or a silicon oxynitride film is provided asan insulating layer 111 covering the gate electrodes, and a siliconnitride film is provided thereon as a barrier layer 112. This siliconnitride film is formed by an RF sputtering method with nitride and argonas sputtering gases, and with silicon as a target, so that an extremelyprecise film can be formed and thereby can be useful as a barrier layer.Further, a planarized inorganic insulating film is provided on thebarrier layer 112 as a planarization layer 113. In this embodiment, SOG(spin on glass) films or inorganic insulating films with a polishedsurface are used as the planarized insulating film.

In this case, a first opening is provided on the source and drainregions 104, 105 in a laminate composed of the gate insulating film 108,insulating layer 111 and barrier layer 112, and a second opening isprovided on the planarization layer 113 to fit on the first openingtherein. Such a structure can be obtained by a method selected from amethod comprising: forming the first opening at the beginning; fillingthe first opening with the planarization layer once; forming the secondopening finally, and a method comprising: providing the planarizationlayer first; forming the second opening; using a new mask to form thefirst opening in the second opening thereafter. However, since a dryetching method is preferably used for forming the first opening, it isdesired to avoid the planarization layer 113 to be exposed to plasma asfar as possible. From this point, it can be said that the former methodis preferable.

Alternatively, the gate wiring 151 and a connection wiring(corresponding to a drain electrode) is connected with the source region104 or the drain region 105 through the first and second openings. Theconnection wiring 114 is a wiring connected to a gate electrode of thedriver TFT 155. A structure in which a wiring containing mainly lowresistance metal such as aluminum or copper is sandwiched by othermetallic films or an alloy film of these metals is preferably used forthe data wiring 152 and the connection wiring 114.

Also, reference numeral 115 denotes a source region of the driver TFT155, with which the power source wiring 153 is connected. In addition,the power source wiring 153 is opposite to a gate wiring 116 of thedriver TFT 155 through the insulating layer 111 and the barrier layer112, so that a storage capacitor 156 a is formed. Further, the gatewiring 116 is opposite to a semiconductor film 117 through the gateinsulating film 108 so that a storage capacitor 156 b is formed. Becausethe power source wiring 153 is connected with a semiconductor layer 118,a charge is supplied therefrom, so that the semiconductor film 117serves as an electrode. Thus, the capacitor portion 156 becomes astructure in which the storage capacitors 156 a and 156 b are connectedin parallel, thereby obtaining a large capacity with a very small area.Furthermore, with respect to particularly the storage capacitor 156 a, asilicon nitride film having a high relative dielectric constant is usedfor dielectric, so that a large capacity can be ensured. Because thedielectric of the storage capacity 156 a is composed of a laminatestructure of the insulating layer 111 and the barrier layer 112, aprobability of occurrence of a pinhole is extremely low. Thus, acapacitor with high reliability can be formed.

When the first and second openings are formed, the number of masks usedin a photolithography process is increased in comparison withconventional cases. However, when the increase in the number of masks isadvantageously used, a new storage capacitor can be formed as describedin this embodiment. Such a point is also one of importantcharacteristics of the present invention. The characteristic of thepresent invention more than compensates for a demerit resulting from theincrease in the number of masks, so that it greatly contributes toindustrial progress. For example, when a high definition image displayis obtained, it is required that a relative occupying area of thestorage capacitor to an area of each pixel is reduced in a displayportion to improve an aperture ratio. Therefore, it is extremely usefulto increase a storage capacity.

Also, in FIG. 1D, reference numeral 119 denotes a drain region of thedriver TFT 155, which is connected with a drain electrode 120. Theelectrode 120 is connected with a pixel electrode 158 to compose apixel. In this embodiment, an oxide conductive film which is transparentwith respect to visible light (typically, an ITO film) is used as thepixel electrode 158. However, the present invention is not limited tosuch a film. In addition, the pixel electrode 158 is formed after theformation of the drain electrode 120, so that the pixel electrode 158 isin contact with the top surface of the drain electrode 120, therebybecomes a structure of being connected with the drain electrode.

An example after the light emitting element 157 is actually formed inthe electroluminescence display device having the above pixel structureis shown in FIG. 2. FIG. 2A is a cross sectional view corresponding tothe cross section shown in FIG. 1C and shows a state in which the lightemitting element 157 is formed on the pixel electrode 158. Note that,when the structure shown in FIG. 2A is used, the pixel electrode 158functions as the anode of the light emitting element 157.

The end portion of the pixel electrode 158, as shown in FIG. 2B, iscovered with a photosensitive organic resin film 121. The photosensitiveorganic resin film 121 is provided in a grid shape so as to frame eachpixel or provided in a stripe shape in row unit or column unit. In anycase, when it is formed on the first and second openings, a concaveportion can be efficiently embedded and the entire surface can be alsoleveled. Note that, the photosensitive organic resin film can be ofpositive type or negative type. Further, a known resist material(polymeric material containing chromophore) can be also used.

Also, although not shown in the figure, if the surface of thephotosensitive organic resin film 121 is covered with a silicon nitridefilm, so that degassing from the photosensitive organic resin film 121can be suppressed. In addition, on the pixel electrode 158, an openingis provided on the photosensitive organic resin film 121, in the openingportion, a light emitting member 122 is in contact with the pixelelectrode 158. The light emitting member 122 is generally composed bylaminating thin films such as a light emitting layer, a carrierinjecting layer, or a carrier transporting layer. However, any structureand material as far as light emissions has been observed can be used.For example, SAlq (in which one of three ligands of Alq₃ is substitutedfor a triphenylsilanol structure) as an organic system materialcontaining silicon can be also used as a charge transporting layer or ahole blocking layer.

Of course, the light emitting layer is not necessarily composed of onlyorganic thin film, and a structure in which an organic thin film and aninorganic thin film are laminated may be also used. A polymeric thinfilm or a monomeric thin film may be used. In addition, a forming methodis changed according to whether a polymer thin film or a low molecularthin film is used. However, the thin film is preferably formed by aknown method.

Also, on the light emitting member 122, an opposing electrode 123 (hereis a cathode) opposing to the pixel electrode 158 is formed via thelight emitting member 122, and a silicon nitride film as a passivationfilm 124 is finally provided thereon. The material for the passivationfilm 124 can be the same as the barrier layer 112. A metallic thin filmcontaining an element belonging to group 1 or 2 of the periodic table ispreferably used as the cathode 124. A metallic film in which lithium of0.2 wt % to 1.5 wt % (preferably, 0.5 wt % to 1.0 wt %) is added toaluminum is suitable in view of a charge injecting property and thelike. Note that, if lithium is diffused, it is concerned that theoperation of a TFT is influenced thereby. However, according to thisembodiment, the TFT is completely protected by the barrier layer 112, sothat it is unnecessary to concern the diffusion of lithium.

When the structures shown in FIGS. 2A and 2B are used, light emittedfrom the light emitting element is emitted from the substrate 101passing through the pixel electrode 158. In this case, since theplanarization layer 113 is of transparent type, the light emitted fromthe light emitting can pass through without problems.

With the electroluminescence display device having such a devicestructure, an influence of plasma damage is reduced, making it possibleto suppress variations in threshold voltage of the transistors and toachieve uniform display characteristics.

Embodiment 2

In this embodiment, description will be given of an example of a devicestructure including the one in which a planarization layer and a barrierlayer are reversed in position in Embodiment 1. Other structures thereofare the same as those in Embodiment 1 and thus, may be attainedreferring to the description of Embodiment 1. Accordingly, thisembodiment will be described focusing on the point different fromEmbodiment 1.

FIGS. 3A and 3B are views corresponding to FIGS. 2A and 2B in Embodiment1, respectively. In the figures, some components are denoted by the samereference symbols as those in Embodiment 1. In this embodiment, aplanarization layer 301 is formed on an insulating layer 111 and asecond opening is formed on the planarization layer 301, after which abarrier layer 302 is formed so as to cover a top surface of theplanarization layer 301 and a side surface (inner wall surface) of thesecond opening. Further, inside the second opening, a gate insulatingfilm 108, the insulating layer 111, and a barrier layer 112 are etchedto form a first opening.

With the structure of this embodiment, the planarization layer 301 canbe completely covered with the insulating layer 111 and the barrierlayer 302 and degassing from the planarization layer 301 can becompletely prevented through sealing. That is, a degassing componentdiffuses neither to a light emitting element side nor to a transistorside, so that a highly reliable display device controlled indeterioration with time can be obtained. Needless to say, similar toEmbodiment 11, an influence of plasma damage is reduced, making itpossible to suppress variations in threshold voltage of the transistorsand to achieve uniform display characteristics.

Embodiment 3

In this embodiment, description will be given of an example of a devicestructure including the one in which a planarization layer and a barrierlayer are reversed in position in Embodiment 1. Other structures thereofare the same as those in Embodiment 1 and thus, may be attainedreferring to the description of Embodiment 1. Accordingly, thisembodiment will be described focusing on the point different fromEmbodiment 1.

FIGS. 4A and 4B are views corresponding to FIGS. 2A and 2B in Embodiment1, respectively. In the figures, some components are denoted by the samereference symbols as those in Embodiment 1. In this embodiment, aplanarization layer 401 is formed on an insulating layer 111 and abarrier layer 402 is formed thereon, after which the barrier layer 302,planarization layer 401, insulating layer 111, and a gate insulatingfilm 108 are etched to form an opening.

With the structure of this embodiment, degassing from the planarizationlayer 401 can be suppressed. That is, suppressing degassing componentsdiffuses to the light emitting element side and to the transistor side,so that a highly reliable display device controlled in deteriorationwith time can be obtained. Needless to say, similar to Embodiment 1, aninfluence of plasma damage is reduced, making it possible to suppressvariations in threshold voltage of the transistors and to achieveuniform display characteristics.

Embodiment 4

This embodiment shown in FIGS. 5A to 5C adopts the device structureseach corresponding to Embodiment 1 to 3, except that nonphotosensitiveorganic resin films 501 to 503 are used as a resin film covering endportions of a pixel electrode 158 by way of example. Other structuresthereof are the same as those in Embodiments 1 to 3 and thus, may beattained referring to descriptions of Embodiments 1 to 3. Accordingly,this embodiment will be described focusing on the point different fromEmbodiments 1 to 3.

When using a photosensitive organic resin film, as shown in FIGS. 2B,3B, and 4B, an upper end portion is curved (with a curvature) and thestructure is useful in increasing a coverage at the time of forming alight emitting member and an opposing electrode. The present invention,however, may not be limited to this. As described in this embodiment,the nonphotosensitive organic resin film can be used without anyproblem. Moreover, when the upper end portion of the resin film coveringthe end portions of the pixel electrode 158 is curved (with thecurvature), if washing the surface of the pixel electrode 158, anyforeign material (such as dust) can be prevented from remaining in thefoot portions thereof.

Note that this embodiment is achieved by partially modifying thestructures of Embodiments 1 to 3, which not impairs the effects ofEmbodiments 1 to 3, but can achieve the similar effects.

Embodiment 5

This embodiment shown in FIGS. 6A to 6C adopts the device structureseach corresponding to Embodiments 1 to 3 except that the structure ofthe active layer of the thin film transistor is changed by way ofexample. Other structures thereof are the same as those of Embodiments 1to 3 and thus, may be attained referring to the description ofEmbodiments 1 to 3. Accordingly, this embodiment will be describedfocusing on the point different from Embodiments 1 to 3.

In FIG. 6A, the active layer of the thin film transistor includes asource region 601 and a drain region 602, and has four LDD (lightlydoped drain) regions and two channel formation regions 603, 604therebetween. The four LDD regions are each obtained by combining twoLDD regions: LDD regions 605 a, 605 b; LDD regions 606 a, 606 b; LDDregions 607 a, 607 b; and LDD regions 608 a, 608 b. Those two regionsare combined to function as the LDD region.

For example, the LDD region 605 a is formed so as to overlap the gateelectrode, whereas the LDD region 605 b is formed so as not to overlapthe gate electrode. In this case, the LDD region 605 a contributes tosuppression of hot carrier degradation, whereas the LDD region 605 bcontributes to reduction of an OFF current (also called a leak current).Those characteristics are well known in the art and reference will bemade of US 2001/0055841 disclosed by the applicants of the presentinvention.

Note that, this embodiment is achieved by partially modifying thestructures of Embodiments 1 to 3, which not impairs the effects ofEmbodiments 1 to 3, but can achieve the similar effects. Also, thisembodiment can be combined with Embodiment 4.

Embodiment 6

This embodiment shown in FIGS. 7A to 7C adopts the device structureseach corresponding to Embodiments 1 to 3 except that the structures ofthe active layer of the thin film transistor and the gate electrodethereof are changed by way of example. Other structures thereof are thesame as those of Embodiments 1 to 3 and thus, may be attained referringto the description of Embodiments 1 to 3. Accordingly, this embodimentwill be described focusing on the point different from Embodiments 1 to3. Note that, the structures of the active layer and the gate electrodeof FIGS. 7A to 7C are the same, so that description will be only made ofthe structures of FIG. 7A.

In FIG. 7A, the active layer of the thin film transistor has a sourceregion 701 and a drain region 702, and has four LDD (lightly dopeddrain) regions 703 a to 703 d and two channel formation regions 704 a,704 b therebetween. Also, the LDD regions 703 a to 703 d arecharacterized in that the regions are formed before forming gateelectrodes 705 and 706. If formed in the stated order, the LDD regionsand the gate electrodes can be designed as to the extent to which theyare overlapped with each other, according to specifications oftransistor characteristics. Therefore, the structures of the activelayer can be made different for each circuit. Those characteristics arewell known in the art and reference will be made of U.S. Pat. No.6,306,694 disclosed by the applicants of the present invention.

Note that, this embodiment is achieved by partially modifying thestructures of Embodiments 1 to 3, which not impairs the effects ofEmbodiments 1 to 3, but can achieve the similar effects. Also, thisembodiment can be combined with Embodiments 4 and 5.

Embodiment 7

This embodiment shown in FIGS. 8A to 8C adopts the device structureseach corresponding to Embodiments 1 to 3 except that the structure ofthe light emitting element is changed by way of example. Otherstructures thereof are the same as those of Embodiments 1 to 3 and thus,may be attained referring to the description of Embodiments 1 to 3.Accordingly, this embodiment will be described focusing on the pointdifferent from Embodiments 1 to 3. Note that the device structures(except the structure of the light emitting element) of FIGS. 8A to 8Care the same, so that description will be only made of the structure ofFIG. 8A.

In FIG. 8A, a pixel electrode 801 is made of a metallic film serving asan anode, which is constituted of gold, platinum, titanium, titaniumnitride, or tungsten. On the pixel electrode 801, as described inEmbodiment 1, the light emitting member 122, the opposing electrode 123serving as a cathode, and a passivation film 124 are formed.

Note that, in this embodiment, an example where the metallic film isused for an anode is shown, but a metallic film serving as a cathode canbe formed instead of forming the anode 801. The metallic film serving asthe cathode may be formed of aluminum (including aluminum added with anelement belonging to Group 1 or 2 in the periodic table, typically, analloy of aluminum and lithium) or an alloy of magnesium and silver. Inthis case, although it is needed to change the structure of the lightemitting member 122 and to form a transparent electrode serving as ananode on the light emitting member 122, both can be attained by usingthe known structures.

Further, in this embodiment, considering the fact that pixel electrodeserves as an anode, the driving TFT is set to a p-channel TFT in itspolarity, but when the pixel electrode is made to serve as a cathode, itis preferable to set the driving TFT to an n-channel TFT in itspolarity.

Note that this embodiment is achieved by partially modifying thestructures of Embodiments 1 to 3, which not impairs the effects ofEmbodiments 1 to 3, but can achieve the similar effects. Also, thisembodiment can be combined with Embodiments 4 to 6.

Embodiment 8

This embodiment shown in FIGS. 9A to 9D adopts the device structurecorresponding to Embodiment 1 except that the connection structures ofthe pixel electrode and the drain electrode are changed by way ofexample. Other structures thereof are the same as those of Embodiment 1and thus, may be attained referring to the description of Embodiment 1.Accordingly, this embodiment will be described focusing on the pointdifferent from Embodiment 1.

A pixel electrode 901 shown in FIG. 9A is connected in contact with alower surface of a drain electrode 902 as shown in FIG. 9D. That is,after forming the planarization layer 113, the pixel electrode 901 maybe formed, followed by forming the drain electrode 902 so as to bepartially overlapped with the pixel electrode 901. Here, the order inwhich the pixel electrode 901 and the drain electrode 902 are formed mayfollow the various methods, as represented by the following two methods.

Firstly, after forming the planarization layer 113, the pixel electrode901 is formed, followed by forming first and second openings in theplanarization layer 113 and then, forming the drain electrode 902.Secondly, after forming the first and second openings in theplanarization layer 113, the pixel electrode 901 and the drain electrode902 are formed in this order. The order may be appropriately set by thedesigner.

Next, FIGS. 10A and 10 B are sectional views corresponding to FIGS. 9Cand 9D, at a point where processing up to the formation of the lightemitting element 157 is completed. The materials etc. for thephotosensitive organic resin film 121, the light emitting member 122,the opposing electrode 123, and the passivation film 124 are asdescribed in Embodiment 1.

Note that this embodiment is achieved by partially modifying thestructures of Embodiment 1, which not impairs the effects of Embodiment1, but can achieve the similar effects. Also, this embodiment can becombined with Embodiments 4 to 7.

Embodiment 9

This embodiment shown in FIGS. 11A and 11B adopts the device structurecorresponding to Embodiment 2 except that the connection structures ofthe pixel electrode and the drain electrode are changed by way ofexample. Other structures thereof are the same as those of Embodiment 2and thus, may be attained referring to the description of Embodiment 2.Also, the same description as in Embodiment 8 may be applied to theconnection relationship between the pixel electrode and the drainelectrode and the order of formation thereof. The above relationship andthe order would be apparent from the description of Embodiment 8.

Note that, this embodiment is achieved by partially modifying thestructures of Embodiment 2, which not impairs the effects of Embodiment2, but can achieve the similar effects. Also, this embodiment can becombined with Embodiments 4 to 7.

Embodiment 10

This embodiment shown in FIGS. 12A and 12B adopts the device structurecorresponding to Embodiment 3 except that the connection structures ofthe pixel electrode and the drain electrode are changed by way ofexample. Other structures thereof are the same as those of Embodiment 3and thus, may be attained referring to the description of Embodiment 3.Also, the same description as in Embodiment 8 may be applied to theconnection relationship between the pixel electrode and the drainelectrode and the order of formation thereof. The above relationship andthe order would be apparent from the description of Embodiment 8.

Note that this embodiment is achieved by partially modifying thestructures of Embodiment 3, which not impairs the effects of Embodiment3, but can achieve the similar effects. Also, this embodiment can becombined with Embodiments 4 to 7.

Embodiment 11

This embodiment shown in FIGS. 13A to 13C adopts the device structureseach corresponding to Embodiments 8 to 10 except that the structure ofthe light emitting element is changed by way of example. Otherstructures thereof are the same as those of Embodiments 8 to 10 andthus, may be attained referring to the description of Embodiments 8 to10. Accordingly, this embodiment will be described focusing on the pointdifferent from Embodiments 8 to 10. Note that, the device structures(except the structure of the light emitting element) of FIGS. 13A to 13Care the same, so that description will be only made of the structure ofFIG. 13A.

In FIG. 13A, a pixel electrode 1301 is made of a metallic film servingas an anode, which is constituted of gold, platinum, titanium, titaniumnitride, or tungsten. On the pixel electrode 1301, as described inEmbodiment 1, the light emitting member 122, the opposing electrode 123serving as a cathode, and the passivation film 124 are formed.

Note that, in this embodiment, an example where the metallic film isused for the anode is shown, but a metallic film serving as a cathodecan be formed instead of forming the anode 1301. The metallic filmserving as the cathode may be formed of aluminum (including aluminumadded with an element belonging to Group 1 or 2 in the periodic table,typically, an alloy of aluminum and lithium) or an alloy of magnesiumand silver. In this case, although it is needed to change the structureof the light emitting member 122 and to form a transparent electrodeserving as the anode on the light emitting member 122, both can beattained by using the known structures.

Further, in this embodiment, considering the fact that pixel electrodeserves as the anode, the driving TFT is set to a p-channel TFT in itspolarity, but when the pixel electrode is made to serve as the cathode,it is preferable to set the driving TFT to an n-channel TFT in itspolarity.

Note that, this embodiment is achieved by partially modifying thestructures of Embodiments 8 to 10, which not impairs the effects ofEmbodiments 8 to 10, but can achieve the similar effects. Also, thisembodiment can be combined with Embodiments 4 to 6 and 8 to 10.

Embodiment 12

This embodiment shown in FIGS. 14A to 14D adopts the device structurecorresponding to Embodiment 1 except that the connection structures ofthe pixel electrode and the drain electrode are changed by way ofexample. Other structures thereof are the same as those of Embodiment 1and thus, may be attained referring to the description of Embodiment 1.Accordingly, this embodiment will be described focusing on the pointdifferent from Embodiment 1.

As shown in FIG. 14A, a planarization layer 1401 is formed on the drainelectrode 120 and a power supply wiring 153, and a pixel electrode 1402is formed on the planarization layer 1401. That is, the pixel electrode1402 is electrically connected with a drain region 119 through a drainelectrode 120 rather than connected in direct contact with the drainregion 119. At this time, an insulating layer 1403 may be made either ofan inorganic insulating film or of an organic insulating film. Needlessto say, the planarization layer made of the SOG film etc. is used as theinsulating layer 1403, which is more effective in improving evenness.

Next, FIGS. 15A and 15B are sectional views corresponding to FIGS. 14Cand 14D, at a point where processing up to the formation of the lightemitting element 157 is completed. The materials etc. for thephotosensitive organic resin film 121, the light emitting member 122,the opposing electrode 123, and the passivation film 124 are asdescribed in Embodiment 1.

Note that this embodiment is achieved by partially modifying thestructures of Embodiment 1, which not impairs the effects of Embodiment1, but can achieve the similar effects. Also, this embodiment can becombined with Embodiments 4 to 7.

Embodiment 13

This embodiment shown in FIGS. 16A and 16B adopts the device structurecorresponding to Embodiment 2 except that the connection structures ofthe pixel electrode and the drain electrode are changed by way ofexample. Other structures thereof are the same as those of Embodiment 2and thus, may be attained referring to the description of Embodiment 2.Also, the same description as in Embodiment 12 may be applied to theconnection relationship between the pixel electrode and the drainelectrode and the order of formation thereof. The above relationship andthe order would be apparent from the description of Embodiment 12.

Note that, this embodiment is achieved by partially modifying thestructures of Embodiment 2, which not impairs the effects of Embodiment2, but can achieve the similar effects. Also, this embodiment can becombined with Embodiments 4 to 7.

Embodiment 14

This embodiment shown in FIGS. 17A and 17B adopts the device structurecorresponding to Embodiment 3 except that the connection structures ofthe pixel electrode and the drain electrode are changed by way ofexample. Other structures thereof are the same as those of Embodiment 3and thus, may be attained referring to the description of Embodiment 3.Also, the same description as in Embodiment 12 may be applied to theconnection relationship between the pixel electrode and the drainelectrode and the order of formation thereof. The above relationship andthe order would be apparent from the description of Embodiment 12.

Note that this embodiment is achieved by partially modifying thestructures of Embodiment 3, which not impairs the effects of Embodiment3, but can achieve the similar effects. Also, this embodiment can becombined with Embodiments 4 to 7.

Embodiment 15

This embodiment shown in FIGS. 18A to 18C adopts the device structureseach corresponding to Embodiments 12 to 14 except that the structure ofthe light emitting element is changed by way of example. Otherstructures thereof are the same as those of Embodiments 12 to 14 andthus, may be attained referring to the description of Embodiments 12 to14. Accordingly, this embodiment will be described focusing on the pointdifferent from Embodiments 12 to 14. Note that the device structures(except the structure of the light emitting element) of FIGS. 18A to 18Care the same, so that description will be only made of the structure ofFIG. 18A.

In FIG. 18A, a pixel electrode 1801 is made of a metallic film servingas an anode, which is constituted of gold, platinum, titanium, titaniumnitride, or tungsten. On the pixel electrode 1801, as described inEmbodiment 1, the light emitting member 122, the opposing electrode 123serving as a cathode, and the passivation film 124 are formed.

Note that, in this embodiment, an example where the metallic film isused for the anode is shown, but a metallic film serving as a cathodecan be formed instead of forming the anode 1801. The metallic filmserving as the cathode may be formed of aluminum (including aluminumadded with an element belonging to Group 1 or 2 in the periodic table,typically, an alloy of aluminum and lithium) or an alloy of magnesiumand silver. In this case, although it is needed to change the structureof the light emitting member 122 and to form a transparent electrodeserving as the anode on the light emitting member 122, both can beattained by using the known structures.

Further, in this embodiment, considering the fact that pixel electrodeserves as the anode, the driving TFT is set to a p-channel TFT in itspolarity, but when the pixel electrode is made to serve as the cathode,it is preferable to set the driving TFT to an n-channel TFT in itspolarity.

Note that this embodiment is achieved by partially modifying thestructures of Embodiments 12 to 14, which not impairs the effects ofEmbodiments 12 to 14, but can achieve the similar effects. Also, thisembodiment can be combined with Embodiments 4 to 6 and 12 to 14.

Embodiment 16

This embodiment shown in FIGS. 19A and 19B adopts the device structureseach corresponding to Embodiment 1 except that the structure of thepixel electrode is changed by way of example. Other structures thereofare the same as those of Embodiment 1 and thus, may be attainedreferring to the description of Embodiment 1. Accordingly, thisembodiment will be described focusing on the point different fromEmbodiment 1.

First, FIG. 19A is a CAD diagram for showing an example of an applicablepixel structure when using an electrode structure of this embodiment.FIG. 19B is a circuit diagram of the CAD diagram of FIG. 19A. Needlessto say, this embodiment is not limited to the pixel structure shown inFIGS. 19A and 19B. In this embodiment, the metallic film is used for thepixel electrode, and light is taken out in a direction opposite to thesubstrate. Therefore, any circuit can be formed below the pixelelectrode without reducing an opening ratio (ratio of an effectivedisplay region to a pixel area) and thus, the pixels can individuallyobtain a variety of functions. Note that the pixel structure shown inFIGS. 19A and 19B is disclosed by the applicants of the presentinvention in the specification of U.S. patent application Ser. No.10/245,711 and is presented as a novel structure according to theinvention by the applicants of the present invention.

Here, the device structure will be more specifically described withreference to FIGS. 20A to 20C. Note that the structure of the thin filmtransistor is the same as that in Embodiment 1 and thus, may be attainedreferring to the description of Embodiment 1. This embodiment differsfrom Embodiment 1 in terms of the structures of data wirings, drainelectrode, and the like formed on the planarization layer 113.

As shown in FIGS. 20A and 20B, on the planarization layer 113, atitanium film 11, a titanium nitride film 12, and an aluminum film 13are formed. The aluminum film 13 is partially removed through etching toexpose the titanium nitride film 12. The aluminum film 13 is etchedusing a resin film 14 as a mask, and the resin film 14 also functionssimilarly to the photosensitive organic resin film 121 in Embodiment 1as it is. Namely, the resin film 14 is formed to cover the abovecomponent exclusive of the portion where the titanium nitride film 12 isexposed. A light emitting member 15 is formed in contact with theportion where the titanium nitride film 12 is exposed and an opposingelectrode 16 and a passivation film 17 are formed thereon.

FIG. 20C is an enlarged view of a region 10 surrounded by the dottedline of FIG. 20B. As shown in FIG. 20C, an etched section of thealuminum film 13 takes a tapered shape having the angle of 30 to 60°(preferably, 45°). That is to say, the angle between the section of thealuminum film and the upper surface thereof is the obtuse angle. Withthis structure, the light emitted from the light emitting member 15 isclassified into three lights: the light directly taken out (directlight); the light taken out after being reflected by the titaniumnitride film (reflection light); and the light taken out afterpropagating laterally in the light emitting member 15 and then, beingreflected by the section of the aluminum film 13 (reflection light). Asa result, as compared with the conventional structure, it can beexpected to increase efficiency in taking out the light.

Note that a TEM (transmission electron microscope) photograph in sectionwhen the pixel electrode is actually formed according to the structureas described above (FIG. 24A) and a schematic diagram thereof (FIG. 24B)are shown. As will be confirmed from the figures, the aluminum filmtakes the tapered shape and the titanium nitride film is exposed.

Also, in this embodiment, the titanium film constitutes a lowest layerso as to enable an ohmic contact with a drain region made of asemiconductor. The titanium nitride film (if its surface is subjected toUV irradiation, a work function increases and thus, this process iseffective) capable of serving as an anode is formed thereon. Further, analuminum film is formed on the top as a reflective electrode forpreventing light leak and thus, a three-layer structure is adopted.However, the present invention is not limited to the above structure,and the provision of a first metallic film serving as an anode(corresponding to the titanium nitride film in this embodiment) and asecond metallic film serving as the reflective electrode (correspondingto the aluminum film in this embodiment) suffices therefor.

Note that this embodiment is achieved by partially modifying thestructures of Embodiment 1, which not impairs the effects of Embodiment1, but can achieve the similar effects. Further, without using an oxideconductive film such as ITO, the metallic film formed as the datawirings etc., is applied to the anode as it is, thereby reducing thenumber of steps. Also, this embodiment can be combined with Embodiments4 to 6 or Embodiment 15 (as a substitute for the pixel electrode 1801).

Embodiment 17

This embodiment shown in FIGS. 21A and 21B adopts the device structurecorresponding to Embodiment 2 except that the structure of the pixelelectrode is changed by way of example. Other structures thereof are thesame as those of Embodiment 2 and thus, may be attained referring to thedescription of Embodiment 2. Also, the same description as in Embodiment16 may be applied to the structure of the pixel electrode. The abovestructure would be apparent from the description of Embodiment 16.

Note that this embodiment is achieved by partially modifying thestructures of Embodiment 2, which not impairs the effects of Embodiment2, but can achieve the similar effects. Also, this embodiment can becombined with Embodiments 4 to 7 and 15.

Embodiment 18

This embodiment shown in FIGS. 22A and 22B adopts the device structurecorresponding to Embodiment 3 except that the structure of the pixelelectrode is changed by way of example. Other structures thereof are thesame as those of Embodiment 3 and thus, may be attained referring to thedescription of Embodiment 3. Also, the same description as in Embodiment16 may be applied to the structure of the pixel electrode. The abovestructure would be apparent from the description of Embodiment 16.

Note that this embodiment is achieved by partially modifying thestructures of Embodiment 3, which not impairs the effects of Embodiment3, but can achieve the similar effects. Also, this embodiment can becombined with Embodiments 4 to 7 and 15.

Embodiment 19

In this embodiment, the structure shown in FIG. 23A is a modifiedstructure of Embodiment 16, in which the barrier layer 23 is formed soas to cover the insulating layer 22 of the driving TFT 21 and the powersupply wiring 24 is formed thereon. Further, the planarization layer 25is formed so as to cover the power supply wiring 24. The film thicknessof the insulating layer 22 may be selected in a range from 0.3 to 1 μm.Through the second opening formed in the planarization layer 25 and thefirst opening formed in each insulating layer under the barrier layer23, the pixel electrode is electrically connected with the driving TFT21. The structures of the pixel electrode and the light emitting elementmay be apparent from the description of Embodiment 16.

The structure shown in FIG. 23B is presented as an example where thebarrier layer is formed in a position different from that of FIG. 23A,which is characterized in that the barrier layer is formed so as tocover the upper surface of the planarization layer 25 and the sidesurface of the second opening. With this structure, the planarizationlayer 25 can be sealed with the insulating layer 22 and the barrierlayer 26, so that the influence of degassing can be further suppressed.

The structure shown in FIG. 23C relates to the combination of thestructures of FIGS. 23A and 23B. In the structure, the barrier layer 23is formed in contact with the lower surface of the planarization layer25 and barrier layer 26 is formed in contact with the upper surfacethereof. With this structure, the planarization layer 25 can be sealedwith the barrier layers 23 and 26, so that the influence of degassingcan be further suppressed.

Note that this embodiment is achieved by partially modifying thestructure of Embodiment 16, which not impairs the effects of Embodiment16, but can achieve the similar effects. Also, this embodiment can becombined with Embodiments 4 to 7.

Embodiment 20

In this embodiment, an example where a size of the first opening is madelarger than that of the second opening in the structure of Embodiment 2is shown. In other words, after forming the insulating layer 111, theinsulating layer 111 and the gate insulating film 108 are etched to formthe first opening, and the planarization layer 301 is formed thereon.Further, the planarization layer 301 is etched to form the secondopening inside the first opening to expose the active layer (sourceregion 104). After the barrier layer 302 is formed so as to cover thesecond opening, a third opening is formed in a portion of the barrierlayer 302 at the bottom portion of the second opening. Accordingly, thedata wirings 151 are connected through the third opening to the sourceregion 104.

When using the structure of this embodiment, in etching theplanarization layer 301, the insulating layer 111 and the gateinsulating film 108 are not exposed to etchant. In particular, the abovestructure is effective when an inorganic insulating film such as an SOGfilm is used for the planarization layer 301, since the insulating layer111 and the gate insulating film 108 are not needed to be etched. Also,if using the SOG film for the planarization layer 301, it is possible toavoid the occurrence of a phenomenon (called poisoned via) in whichmoisture emitted from the planarization layer causes the wiringmaterials to corrode.

Note that this embodiment can be combined not only with the structure ofEmbodiment 1 but also with those of Embodiments 2 to 11, and 16 to 18.

Embodiment 21

In this embodiment, an example where the shape of the etched section ofthe drain electrode differs from the shape of Embodiment 9 is shown.That is, as shown in FIGS. 26A and 26B, as the characteristics of thisembodiment, the section in etching takes a reversely tapered shape. InFIG. 26A, reference numerals 31 and 32 denote a drain electrode and apower supply wiring for an adjacent pixel, respectively. FIG. 26B is anenlarged view of a region 33 surrounded by the dotted line of FIG. 26A.

As shown in FIG. 26B, the light emitted from the light emitting member122 is classified into the direct light, the reflection light reflectedby the cathode 123, and the reflection light reflected by the powersupply wiring 32. Those lights can be recognized by an observer. In thisway, an increase in efficiency in taking out the light is achieved as aneffect of this embodiment.

Note that, this embodiment can be combined not only with the structureof Embodiment 9 but also with those of Embodiments 4 to 6, 8, and 10.

Embodiment 22

In this embodiment, an example in which the structure of the pixelelectrode differs from that of Embodiment 2 is shown. That is, as shownin FIG. 27A, the laminate electrode composed of the first metallic film(preferably, aluminum film) 41 and the second metallic film (preferably,titanium nitride film) 42 is formed as the pixel electrode. Thephotosensitive organic resin film 121 is formed so as to cover the endportions thereof, on which the oxide conductive film (preferably, ITOfilm) 43 is formed. Thus, the finally defined light emitting regioncorresponds to a contact portion between the oxide conductive film 43and the light emitting member 122.

Also, the structure shown in FIG. 27B is presented as an example wherethe second metallic film 42 is formed after forming the photosensitiveorganic resin film 121 and the oxide conductive film 43 and the secondmetallic film 42 are laminated as shown in FIG. 27A. In this case, thefinally defined light emitting region corresponds to a contact portionbetween the second metallic film 42 and the oxide conductive film 43 andalmost the entire region in the pixel can be used as the light emittingregion.

As described above, according to this embodiment, the pixel area can beeffectively used and the opening ratio can be increased, therebyachieving the high-luminance display. Also, the luminance as high as theconventional ones realize is obtained with less power consumption, sothat the highly reliable display device can be provided.

Note that this embodiment can be implemented in combination with thedevice structures described in Embodiments 1 to 3 (structures before thepixel electrode is formed) as well as the structures of Embodiments 4 to6.

Embodiment 23

The structures of the thin film transistor described in Embodiments 1 to22 all become top-gate structures (specifically, planar structures). Ineach embodiment (except Embodiment 6), however, a bottom-gate structure(typically, reverse stagger structure) can be adopted as well. Moreover,the application thereof is not limited to the thin film transistor butmay be made of a MOS transistor formed by using silicon well.

Embodiment 24

The display devices shown in Embodiments 1 to 22 each exemplify anelectroluminescence display device. However, the device structure itself(before the pixel electrode is formed) is similar to the case ofapplying the device structure to a liquid crystal display device. Inaddition, the device structure may be applied to the display devicessuch as the liquid crystal display device and the field emission displaydevice.

Embodiment 25

In this embodiment, a structure of the entire electroluminescencedisplay device to which the present invention is applicable will bedescribed with FIGS. 28A to 28D. FIG. 28A is a top view of anelectroluminescence display device formed by sealing an elementsubstrate in which thin film transistors are formed with a sealingmaterial. FIG. 28B is a cross sectional view along a line B-B′ in FIG.28A. FIG. 28C is a cross sectional view along a line A-A′ in FIG. 28A.

A pixel portion (display portion) 202, a data line driver circuit 203,gate line driver circuits 204 a and 204 b, and a protective circuit 205,which are provided to surround the pixel portion 202, are all located ona substrate 201, and a seal material 206 is provided to surround allthese. The structure of the pixel portion 202 preferably refers toEmbodiments 1 to 23 and the description thereof. As the seal material206, a glass material, a metallic material (typically, a stainlessmaterial), a ceramic material, or a plastic material (including aplastic film) can be used. As shown in Embodiments 1 to 24, it can bealso sealed with only an insulating film. In addition, it is necessaryto use a translucent material according to a radiation direction oflight from an EL element.

The seal material 206 may be provided to partially overlap with the dataline driver circuit 203, the gate line driver circuits 204 a and 204 b,and the protective circuit 205. A sealing material 207 is provided usingthe seal material 206, so that a closed space 208 is formed by thesubstrate 201, the seal material 206, and the sealing material 207. Ahygroscopic agent (barium oxide, calcium oxide, or the like) 209 isprovided in advance in a concave portion of the sealing material 207, sothat it has a function of absorbing moisture, oxygen, and the like tokeep an atmosphere clean in an inner portion of the above closed space208, thereby suppressing the deterioration of an EL layer. The concaveportion is covered with a cover material 210 with a fine mesh shape. Thecover material 210 allows air and moisture to pass therethrough but notthe hygroscopic agent 209. Note that the closed space 208 is preferablyfilled with a noble gas such as nitrogen or argon, and can be alsofilled with a resin or a liquid if it is inert.

Also, an input terminal portion 211 for transmitting signals to the dataline driver circuit 203 and the gate line driver circuits 204 a and 204b is provided on the substrate 201. Data signals such as video signalsare transferred to the input terminal portion 211 through a FPC(flexible printed circuit) 212. With respect to a cross section of theinput terminal portion 211, as shown in FIG. 28B, an input wiring havinga structure in which an oxide conductive film 214 is laminated on awiring 213 formed together with a gate wiring or a data wiring iselectrically connected with a wiring 215 provided in the FPC 212 sidethrough a resin 217 to which conductors 216 are dispersed. Note that aspherical polymer compound for which plating processing using gold orsilver is conducted is preferably used for the conductors 216.

Also, an enlarged view of a region 218 surrounded by a dot line in FIG.28C is shown in FIG. 28D. The protective circuit 205 is preferablycomposed by combining a thin film transistor 219 and a capacitor 220,and any known structure may be used therefor. The present invention hassuch a feature that the formation of the capacitor is possible withoutincreasing the number of photolithography steps together with theimprovement of contact holes. In this embodiment, the capacitor 220 isformed utilizing the feature. Note that the structure of the thin filmtransistor 219 and that of the capacitor 220 can be understood byreferring with Embodiment 1 and description thereof, and therefore thedescription is omitted here.

In this embodiment, the protective circuit 205 is provided between theinput terminal portion 211 and the data line driver circuit 203. When anelectrostatic signal such as an unexpected pulse signal is inputtedtherebetween, the protective circuit releases the pulse signal to theoutside. At this time, first, a high voltage signal which isinstantaneously inputted can be dulled by the capacitor 220, and otherhigh voltages can be released to the outside through a circuit composedof a thin film transistor and a thin film diode. Of course, theprotective circuit may be provided in other location, for example, alocation between the pixel portion 202 and the data line driver circuit203 or locations between the pixel portion 202 and the gate line drivercircuits 204 a and 204 b.

As described above, according to this embodiment, when the presentinvention is carried out, an example in which the capacitor used for theprotective circuit for electrostatic measures and the like which isprovided in the input terminal portion is simultaneously formed isindicated. This embodiment can be carried out by being combined with anystructure of Embodiments 1 to 23.

Embodiment 26

Examples of electronic apparatuses employing a display device of thepresent invention to a display portion therein can be given as a videocamera, a digital camera, a goggle type display (head mounted display),a navigation system, an audio reproducing apparatus (car audio, an audiocomponent, and the like), a laptop computer, a game machine, a portableinformation terminal (a mobile computer, a cellular phone, a portablegame machine, an electronic book, etc.), and an image reproducingapparatus including a recording medium (specifically, an apparatuscapable of processing data in a recording medium such as a DigitalVersatile Disk (DVD) and having a display that can display the image ofthe data). Practical examples thereof are shown in FIGS. 29A to 29H.

FIG. 29A shows a television, which comprises a casing 2001, a supportingbase 2002, a display portion 2003, speaker units 2004, a video inputterminal 2005, etc. The present invention is applied to the displayportion 2003. The term television includes every television fordisplaying information such as one for a personal computer, one forreceiving TV broadcasting, and one for advertisement.

FIG. 29B shows a digital camera, which comprises a main body 2101, adisplay portion 2102, an image receiving unit 2103, operation keys 2104,an external connection port 2105, a shutter 2106, etc. The presentinvention is applied to the display portion 2102.

FIG. 29C shows a laptop computer, which comprises a main body 2201, acasing 2202, a display portion 2203, a keyboard 2204, an externalconnection port 2205, a pointing mouse 2206, etc. The present inventionis applied to the display portion 2203.

FIG. 29D shows a mobile computer, which comprises a main body 2301, adisplay portion 2302, a switch 2303, operation keys 2304, an infraredray port 2305, etc. The present invention is applied to the displayportion 2302.

FIG. 29E shows a portable image reproducing apparatus equipped with arecording medium (a DVD player, to be specific). The apparatus comprisesa main body 2401, a casing 2402, a display portion A 2403, a displayportion B 2404, a recording medium (such as DVD) reading unit 2405,operation keys 2406, speaker units 2407, etc. The display portion A 2403mainly displays image information whereas the display portion B 2404mainly displays text information. The present invention is applied tothe display portions A 2403 and B 2404. The term image reproducingapparatus equipped with a recording medium includes domestic gamemachines.

FIG. 29F shows a goggle type display (head mounted display), whichcomprises a main body 2501, display portions 2502, and arm units 2503.The present invention is applied to the display portion 2502.

FIG. 29G shows a video camera, which comprises a main body 2601, adisplay portion 2602, a casing 2603, an external connection port 2604, aremote control receiving unit 2605, an image receiving unit 2606, abattery 2607, an audio input unit 2608, operation keys 2609, etc. Thepresent invention is applied to the display portion 2602.

FIG. 29H shows a cellular phone, which comprises a main body 2701, acasing 2702, a display portion 2703, an audio input unit 2704, an audiooutput unit 2705, operation keys 2706, an external connection port 2707,an antenna 2708, etc. The present invention is applied to the displayportion 2703. If the display portion 2703 displays white characters on ablack background, power consumption of the cellular phone can bereduced.

As described above, the display device obtained by implementing thepresent invention may be used as the display portions of any electronicapparatus. The electronic apparatuses of the present Embodiment may useany structure of the display device shown in Embodiments 1 to 25.

Consequently, the display device is formed based on the device structureaccording to the present invention, whereby the influence of the plasmadamage can be reduced in the manufacturing steps thereof, the variationsof the threshold voltage of the transistors can be suppressed, and thedisplay device having the uniform display characteristics can beobtained.

1. A display device comprising: a thin film transistor comprising: asemiconductor film; a first insulating film over the semiconductor film;and a gate electrode over the first insulating film; a second insulatingfilm over the thin film transistor, wherein the second insulating filmis a silicon nitride film; a planarization film over the secondinsulating film, wherein the planarization film has a first openingportion; a first electrode over the planarization film and in the firstopening portion, wherein the first electrode is electrically connectedto the thin film transistor; an organic resin film over the firstelectrode, wherein the organic resin film has a second opening portion;a light-emitting member over the first electrode and the organic resinfilm; a second electrode over the light-emitting member, wherein a firstedge portion of the first opening portion is rounded, wherein a secondedge portion of the second opening portion is rounded, wherein theorganic resin film is provided in the first opening portion, wherein abottom of the second opening portion does not overlap with a bottom ofthe first opening portion.
 2. The display device according to claim 1,further comprising a third insulating film over the second electrode,wherein the third insulating film is a silicon nitride film.
 3. Thedisplay device according to claim 1, wherein the first insulating filmis a silicon oxynitride film.
 4. The display device according to claim1, wherein the gate electrode is a tantalum nitride film.
 5. The displaydevice according to claim 1, wherein the gate electrode is a tungstenfilm.
 6. The display device according to claim 1, wherein theplanarization film is an inorganic insulating film.
 7. The displaydevice according to claim 1, further comprising a third electrode overthe second insulating film, wherein the third electrode electricallyconnects the first electrode and the semiconductor film.
 8. The displaydevice according to claim 1, wherein the first electrode is atransparent oxide conductive film.
 9. The display device according toclaim 1, wherein the organic resin film is a photosensitive organicresin film.
 10. An electronic apparatus comprising: an audio outputunit; and the display device according to claim
 1. 11. The electronicapparatus according to claim 10, wherein the electronic apparatus is acellular phone.
 12. An electronic apparatus comprising the displaydevice according to claim 1, wherein the display device is incorporatedin at least one selected from the group consisting of a television, adigital camera, a personal computer, a mobile computer, an imagereproducing apparatus, a goggle-type display, a video camera, and acellular phone.
 13. A display device comprising: a thin film transistorcomprising: a semiconductor film; a first insulating film over thesemiconductor film; and a gate electrode over the first insulating film;a second insulating film over the thin film transistor; a planarizationfilm over the second insulating film, wherein the planarization film hasa first opening portion; a first electrode over the planarization filmand in the first opening portion, wherein the first electrode iselectrically connected to the thin film transistor; an organic resinfilm over the first electrode, wherein the organic resin film has asecond opening portion; a light-emitting member over the first electrodeand the organic resin film; a second electrode over the light-emittingmember, wherein a first edge portion of the first opening portion isrounded, wherein a second edge portion of the second opening portion isrounded, wherein the organic resin film is provided in the first openingportion, wherein a bottom of the second opening portion does not overlapwith a bottom of the first opening portion.
 14. The display deviceaccording to claim 13, further comprising a third insulating film overthe second electrode, wherein the third insulating film is a siliconnitride film.
 15. The display device according to claim 13, wherein thefirst insulating film is a silicon oxynitride film.
 16. The displaydevice according to claim 13, wherein the gate electrode is a tantalumnitride film.
 17. The display device according to claim 13, wherein thegate electrode is a tungsten film.
 18. The display device according toclaim 13, wherein the planarization film is an inorganic insulatingfilm.
 19. The display device according to claim 13, further comprising athird electrode over the second insulating film, wherein the thirdelectrode electrically connects the first electrode and thesemiconductor film.
 20. The display device according to claim 13,wherein the first electrode is a transparent oxide conductive film. 21.The display device according to claim 13, wherein the organic resin filmis a photosensitive organic resin film.
 22. An electronic apparatuscomprising: an audio output unit; and the display device according toclaim
 13. 23. The electronic apparatus according to claim 22, whereinthe electronic apparatus is a cellular phone.
 24. The display deviceaccording to claim 13, wherein the display device is incorporated in atleast one selected from the group consisting of a television, a digitalcamera, a personal computer, a mobile computer, an image reproducingapparatus, a goggle-type display, a video camera, and a cellular phone.25. A display device comprising: a thin film transistor formed over asubstrate, wherein the thin film transistor comprises a semiconductorfilm and a gate electrode with a gate insulating film interposedtherebetween; a insulating layer formed over the gate electrode; abarrier layer formed over the insulating layer, wherein the barrierlayer is a silicon nitride film; a pixel electrode formed over thebarrier layer; an electrode over the pixel electrode, wherein theelectrode comprises a reflective material; a resin film formed over thepixel electrode and the electrode; and a light emitting member formedover the pixel electrode, the electrode, and the resin film, wherein anedge portion of the electrode has a tapered shape.
 26. The displaydevice according to claim 25, wherein the electrode comprises aluminum.27. The display device according to claim 25, wherein the pixelelectrode is a titanium nitride film.
 28. The display device accordingto claim 25, wherein the tapered shape has an angle of 30° to 60°. 29.The display device according to claim 25, wherein the insulating layeris a silicon nitride film or a silicon oxynitride film.
 30. The displaydevice according to claim 25, wherein the pixel electrode is an oxideconductive film.
 31. The display device according to claim 25, whereinthe gate electrode comprises tungsten.
 32. The display device accordingto claim 25, wherein the gate insulating film is a silicon oxynitridefilm.
 33. The display device according to claim 25, wherein the displaydevice is incorporated in at least one selected from the groupconsisting of a television, a digital camera, a personal computer, amobile computer, an image reproducing apparatus, a goggle-type display,a video camera, and a cellular phone.